Definition of Carcinogen

Carcinogen: A substance or agent that causes cancer. Related terms include the adjective "carcinogenic" and the nouns "carcinogenesis" and "carcinogenicity." One of the best-known carcinogens is ionizing radiation.

The International Agency for Research on Cancer has classified some 60 substances and processes as probably or definitely carcinogenic in humans. These substances and processes are divided into three categories -- Agents and groups of agents, Mixtures, and Exposure circumstances -- and they are as follows: